In-plane field-induced vortex liquid correlations in underdoped Bi_2Sr_2CaCu_2O_8+\delta

TL;DR

This study investigates how in-plane magnetic fields influence vortex liquid correlations and Josephson plasma oscillations in underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+eta}$, revealing state-dependent effects on plasma resonance.

Contribution

It demonstrates the contrasting effects of in-plane magnetic fields on Josephson plasma resonance in vortex solid and liquid phases, highlighting vortex interactions in high-temperature superconductors.

Findings

In-plane magnetic fields depress JPR in vortex solid phase.

In-plane magnetic fields can enhance JPR in vortex liquid phase.

Enhanced plasma resonance correlates with absence of vortex pinning near melting line.

Abstract

The effect of a magnetic field component parallel to the superconducting layers on longitudinal Josephson plasma oscillations in the layered high temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is shown to depend on the thermodynamic state of the underlying vortex lattice. Whereas the parallel magnetic field component depresses the Josephson Plasma Resonance (JPR) frequency in the vortex solid phase, it may enhance it in the vortex liquid. There is a close correlation between the behavior of microwave absorption near the JPR frequency and the effectiveness of pancake vortex pinning, with the enhancement of the plasma resonance frequency occurring in the absence of pinning, at high temperature close to the vortex melting line. An interpretation is proposed in terms of the attraction between pancake vortices and Josephson vortices, apparently also present in the vortex liquid state.